Subterranean cavities, such as manholes or wetwells are usually lined with concrete, brick, wood, plastic or other materials. With the passage of time, the lining material deteriorates and eventually requires repair or replacement. In the past, workers have needed to descend into the manhole and rejuvenate it by applying concrete, plaster, gunnite, tar, paint, and other materials to the inner walls of the manhole. Such prior art repair techniques are labor-intensive and expensive. Moreover, it is difficult to completely clean the surface of the manhole walls before applying the repair material. As a result, the repair material often does not adequately adhere to such surfaces. Clumps of the repair material eventually separate from the walls and may fall into the effluent flowing through the manhole, and the repair job must then be repeated.
Especially in locations where the water table is high, water and silt tend to infiltrate the manhole through defects such as apertures and cracks formed therein. If the repair material falls into the effluent, it may enter pumps at a waste water treatment plant, thereby damaging the pumps and necessitating another costly repair or replacement effort. Over the years, the expensive cycle of patchwork repair, detachment of the repair material and repair or replacement of pumps has been repeated throughout the world because adequate repair techniques simply have not been available until now.
Influx of silt and water creates an additional problem because every drop of water entering a waste water treatment plant must be treated. Since waste water treatment plants are expensive to build and operate, any wasted capacity which is dedicated to treating ground water entering the sewer system through defective manholes needs to be eliminated.
Thus far, the only practical alternative to patchwork repair methods has been excavation, followed by the complete removal and replacement of the manhole. This has not been the repair method of choice, in part because of its expense and in part because of the traffic tie-ups and public inconvenience usually associated with the excavation process.
The patchwork repair and the complete replacement methods are primarily addressed to vertically-oriented cavities such as manholes and wetwells. In contrast, a repair method having utility in connection with the repair of horizontally extending underground pipes, rather than vertically extending manholes, is disclosed in U.S. Pat. No. 4,581,085 to Wood. In that disclosure, an inverted liner needs to be introduced into a pipe by a pull chord or wire. Using a feed tube and lubricant, numerous method steps are required to evert the liner into position within the pipe without sticking or tearing of the liner.